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Assumptions Used to Estimate Fair Value of Stock Options Granted (Detail) (USD $)
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12 Months Ended | ||
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Dec. 31, 2011
Year
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Dec. 31, 2010
Year
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Dec. 31, 2009
Year
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| Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items] | |||
| Dividend yield | 1.80% | 0.50% | 0.60% |
| Expected volatility | 32.70% | 29.90% | 32.30% |
| Risk-free interest rate | 1.20% | 1.60% | 2.00% |
| Expected term (in years) | 4.8 | 4.6 | 4.6 |
| Weighted-average fair value of stock options granted | $ 7.85 | $ 8.28 | $ 7.90 |
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- Details
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- Definition
The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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